libmongoc库和libbson库的使用
学习一项知识，最好的方式是查看官方说明书。
测试环境：
操作系统：Windows 10 x64
MongoDB版本：mongodb-5.0.14
MongoDB Client Library版本：libmongoc 1.23.1
前言
工作和学习过程中，需要用到数据库，这里挑选了MongoDB 非关系型数据库。使用数据库，肯定离不开数据库的 增、删、改、查。
MongoDB自带了客户端程序：mongosh.exe，基本可以满足用户所有的操作需要。但是进行程序二次开发，我们还是需要使用 MongoDB Client Library.
本文主要介绍 libmongoc库 和 libbson库的常用函数，以及使用过程中的注意事项
一、libmongoc库和libbson库的介绍
官网介绍：
A Cross Platform MongoDB Client Library for C
The MongoDB C Driver, also known as “libmongoc”, is a library for using MongoDB from C applications, and for writing MongoDB drivers in higher-level languages.
It depends on libbson to generate and parse BSON documents, the native data format of MongoDB.
MongoDB的数据存储格式：bson ，那么就需要libbson库。
数据库原始数据：
{"id":1001,"name":"ZhangSan","age":18,"sex":"male","Chinese":93.0,"Math":100.0,"English":80.0}
{"id":1002,"name":"LiSi","age":18,"sex":"male","Chinese":100.0,"Math":60.0,"English":80.0}
{"id":1003,"name":"WangWu","age":19,"sex":"male","Chinese":90.0,"Math":100.0,"English":90.0}
{"id":1004,"name":"ZhaoLiu","age":19,"sex":"male","Chinese":95.0,"Math":70.0,"English":80.0}
{"id":1005,"name":"XiaoLi","age":18,"sex":"female","Chinese":100.0,"Math":100.0,"English":80.0}
二、libmongoc库的使用
数据库的CRUD(即create、read、update、delete)操作
2-1 create（增操作）
以json格式传入，在表中创建一条bson。
实现代码
#include <mongoc/mongoc.h>
static int lib_collection_create_document(const char *uri_string, const char *database_name, const char *collection_name, const char *json)
{
mongoc_client_t *client = NULL;
mongoc_collection_t *collection = NULL;
bson_error_t error;
bson_oid_t oid;
bson_t *doc = NULL;
bson_t *json_d = NULL;
int result = 0;
/* create mongoc client instace */
client = mongoc_client_new(uri_string);
/* create collection instace */
collection = mongoc_client_get_collection(client, database_name, collection_name);
/* create bson instace */
doc = bson_new();
/* init bson oid.
* oid is primary key in collection
*/
bson_oid_init(&oid, NULL);
/* bson oid append bson_t */
BSON_APPEND_OID(doc, "_id", &oid);
json_d = bson_new_from_json((unsigned char *)json, -1, &error);
if (!json_d)
{
fprintf(stderr, "%s\n", error.message);
result = -1;
}
bson_concat(doc, json_d);
bson_destroy(json_d);
if (!mongoc_collection_insert_one(collection, doc, NULL, NULL, &error))
{
fprintf(stderr, "%s\n", error.message);
result = -2;
}
/* free bson_t memory */
bson_destroy(doc);
/* free mongoc_collection_t */
mongoc_collection_destroy(collection);
/* free mongoc_client_t */
mongoc_client_destroy(client);
return result;
}
int main(int argc, char *argv[])
{
mongoc_init();
const char *uri_string = "mongodb://10.8.198.55:27017";
const char *database = "event_database";
const char *collection = "student_coll";
// add a json to collection
// 注意：若将"XiaoHong" 替换为中文 "小红" , 在 json 转换 bson 过程中，会报错。
// 若需要插入中文字符串，则需要将ansi编码转换成utf-8编码，才能避免报错
char json[500] = {"{\"id\":1006,\"name\":\"XiaoHong\",\"age\":24,\"sex\":\"female\",\"Chinese\":74.0,\"Math\":85.0,\"English\":81.0}"};
if (0 == lib_collection_create_document(uri_string, database, collection, json))
{
printf("Create successful : %s\n", json);
}
mongoc_cleanup();
return 0;
}
运行结果：
💡 函数介绍：*bson_t *bson_new_from_json (const uint8_t *data, ssize_t len, bson_error_t *error);
2-2 read（查操作）
在表中查找符合条件的document，通过数组返回
实现代码：
#include <mongoc/mongoc.h>
static int lib_collection_read_document(const char *uri_string, const char *database_name, const char *collection_name, const char *json_opts,
char doc_list_arr[][300], int *num_of_docs)
{
mongoc_client_t *client = NULL;
mongoc_collection_t *collection = NULL;
mongoc_cursor_t *cursor = NULL;
bson_error_t error;
const bson_t *doc = NULL;
bson_t *query = NULL;
bson_t *json_d = NULL;
char *str = NULL;
int result = 0;
client = mongoc_client_new(uri_string);
collection = mongoc_client_get_collection(client, database_name, collection_name);
query = bson_new();
json_d = bson_new_from_json((unsigned char *)json_opts, -1, &error);
if (!json_d)
{
fprintf(stderr, "%s\n", error.message);
result = -1;
}
bson_concat(query, json_d);
bson_destroy(json_d);
cursor = mongoc_collection_find_with_opts(collection, query, NULL, NULL);
while (mongoc_cursor_next(cursor, &doc))
{
//str = bson_as_canonical_extended_json(doc, NULL);
//str = bson_as_relaxed_extended_json(doc, NULL);
str = bson_as_json(doc, NULL);
sprintf(doc_list_arr[*num_of_docs], "%s", str);
(*num_of_docs)++;
bson_free(str);
}
bson_destroy(query);
mongoc_cursor_destroy(cursor);
mongoc_collection_destroy(collection);
mongoc_client_destroy(client);
return result;
}
int main(int argc, char *argv[])
{
mongoc_init();
const char *uri_string = "mongodb://10.8.198.55:27017";
const char *database = "event_database";
const char *collection = "student_coll";
/* read jsons from collection with options */
char json_opts[300] = {"{\"age\":18,\"sex\":\"male\"}"};
char doc_list_arr[100][300] = {0};
int num_of_docs = 0;
lib_collection_read_document(uri_string, database, collection, json_opts, doc_list_arr, &num_of_docs);
for (int i = 0; i < num_of_docs; i++)
{
printf("%s\n", doc_list_arr[i]);
}
mongoc_cleanup();
return 0;
}
运行结果：
2-3 update（改操作）
在表中查找指定的json，符合条件的json进行修改
注意：这里修改值的类型为string
实现代码：
#include <mongoc/mongoc.h>
#include <bson/bson.h>
static int lib_collection_update_document(const char *uri_string, const char *database_name, const char *collection_name, const char *json_opts,
const char *key, const char *value_string)
{
mongoc_collection_t *collection = NULL;
mongoc_client_t *client = NULL;
bson_error_t error;
mongoc_cursor_t *cursor = NULL;
const bson_t *doc = NULL;
bson_t *update = NULL;
bson_t *query = NULL;
int result = 0;
client = mongoc_client_new(uri_string);
collection = mongoc_client_get_collection(client, database_name, collection_name);
update = BCON_NEW("$set",
"{",
key,
BCON_UTF8(value_string),
"}");
query = bson_new_from_json((unsigned char *)json_opts, -1, &error);
if (!query)
{
fprintf(stderr, "%s\n", error.message);
result = -1;
}
cursor = mongoc_collection_find_with_opts(collection, query, NULL, NULL);
while (mongoc_cursor_next(cursor, &doc))
{
if (!mongoc_collection_update_one(collection, doc, update, NULL, NULL, &error))
{
fprintf(stderr, "%s\n", error.message);
result = -2;
break;
}
}
bson_destroy(query);
bson_destroy(update);
mongoc_cursor_destroy(cursor);
mongoc_collection_destroy(collection);
mongoc_client_destroy(client);
return result;
}
int main(int argc, char *argv[])
{
mongoc_init();
const char *uri_string = "mongodb://10.8.198.55:27017";
const char *database = "event_database";
const char *collection = "student_coll";
/* update documents from collection wiht options */
char json_opts[300] = { "{\"id\":1006}" };
const char *key = "name";
const char *value = "XiaoHe";
if (0 == lib_collection_update_document(uri_string, database, collection, json_opts, key, value))
{
printf("Update successful\n");
}
mongoc_cleanup();
return 0;
}
运行结果：
2-4 delete（删操作）
在表中查找指定的json，符合条件的json进行删除
实现代码：
#include <mongoc/mongoc.h>
#include <bson/bson.h>
static int lib_collection_delete_document(const char *uri_string, const char *database_name, const char *collection_name, const char *json_opts)
{
mongoc_client_t *client = NULL;
mongoc_collection_t *collection = NULL;
mongoc_cursor_t *cursor = NULL;
bson_error_t error;
const bson_t *doc = NULL;
bson_t *query = NULL;
int result = 0;
client = mongoc_client_new(uri_string);
collection = mongoc_client_get_collection(client, database_name, collection_name);
query = bson_new_from_json((unsigned char *)json_opts, -1, &error);
if (!query)
{
fprintf(stderr, "%s\n", error.message);
result = -1;
}
cursor = mongoc_collection_find_with_opts(collection, query, NULL, NULL);
while (mongoc_cursor_next(cursor, &doc))
{
if (!mongoc_collection_delete_one(collection, doc, NULL, NULL, &error))
{
fprintf(stderr, "%s\n", error.message);
result = -2;
}
}
bson_destroy(query);
mongoc_cursor_destroy(cursor);
mongoc_collection_destroy(collection);
mongoc_client_destroy(client);
return result;
}
int main(int argc, char *argv[])
{
mongoc_init();
const char *uri_string = "mongodb://10.8.198.55:27017";
const char *database = "event_database";
const char *collection = "student_coll";
/* delete documents with options in collection */
char json_opts[300] = { "{\"age\":19}" };
if (0 == lib_collection_delete_document(uri_string, database, collection, json_opts))
{
printf("Delete successful\n");
}
mongoc_cleanup();
return 0;
}
运行结果：
三、libbson库的使用
-
将bson格式转换成json格式（value不带类型）
函数：char * bson_as_json (const bson_t *bson, size_t *length);
输出格式：
注意事项：函数返回值（指针）记得使用函数
void bson_free (void *mem)释放 -
将bson格式转换成json格式（value带类型）
函数：char * bson_as_canonical_extended_json (const bson_t *bson, size_t *length)
输出格式：
注意事项：函数返回值（指针）记得使用函数
void bson_free (void *mem)释放
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